Rabbit polyclonal to PCDHB10

The sexual plasticity of the gonads is not retained after the completion of sex differentiation in vertebrates, except in some hermaphroditic species. fish maintain their sexual plasticity until adulthood and E2 plays a critical role in maintaining the female phenotype. Vertebrates have various mechanisms of sex determination, from genetic to environmental, but they all seem to have a neutral stage during embryonic development where 908112-43-6 the gonad is bipotential, and subsequently follows a sex differentiating pathway oriented towards either ovary or testis development. A large number of studies in fishes as well as other higher vertebrates suggest that during the period of sex differentiation, treatment with exogenous sex steroids such as estrogens or androgens causes sex reversal, but these steroids are effective only in early juveniles whose gonads are not 908112-43-6 sexually differentiated1. With the exception of various hermaphroditic fishes, reptiles and amphibians, the general consensus until recently was that gonochoristic vertebrates completely lose their sexual plasticity after differentiation of the gonad into either ovary or testis. However, a recent paper2 published during the progression of this research showed that type A spermatogonia isolated from cryopreserved whole testes of rainbow trout (inhibition of aromatase, the terminal Rabbit polyclonal to PCDHB10 enzyme responsible for E2 production, with highly specific aromatase inhibitors (AI). We used fadrozole (Fd) for tilapia and exemestane (EM) for medaka. The efficacy of Fd and EM in the induction of testicular differentiation in embryos of several non-mammalian vertebrates has already been proven10,11. Adult breeding females of tilapia (one year old) and medaka (5 months old) were exposed to Fd and EM, respectively, until complete sex-reversal was achieved (6 months in tilapia and 2 months in medaka). The tilapia were fed a diet mixed with 200?g/g Fd, while for medaka, 100?g/L EM was added to the water in which the fish were reared. Very intriguingly, our results revealed for the first time in any vertebrate species that both tilapia and medaka females retain their sexual plasticity even in the adult stage. Furthermore, the present data indicate that estrogens are vital to the maintenance of female phenotype in the gonochoristic species. Results E2 depletion induces male-specific gonadal phenotype in adult genetic female tilapia In all adult breeding females of tilapia treated with AI alone, plasma levels of E2 were significantly lower than those of the control groups (Fig. 1a and c). In contrast, no discernible changes were seen in the levels of 11-KT in fish at 60 (data not shown) and 90 days of treatment (dot) (Fig. 1b). Significant increases in plasma levels of 11-KT were observed in female tilapia at 180 dot (Fig. 1d). In contrast, the plasma E2 908112-43-6 and 11-KT levels in fish with co-treatment of E2 were comparable to those of the controls (Fig. 1a to d). Figure 1 Effects of aromatase inhibition on synthesis of sex steroids and ovarian morphology. Ovaries of exposed tilapia were analyzed periodically to detect testicular tissue. Gonads of untreated- and vehicle-controls contained numerous postvitellogenic follicles (untreated control, Fig. 1e and f; vehicle, data not shown). There was no indication of an extensive morphological change until 90 dot in ovaries of tilapia, although the degeneration of some vitellogenic follicles (Fig. 1g) and the appearance of small spermatogonial cysts were apparent. By 180 dot, almost all AI-treated fish had sex-reversed gonads with spermatogenic germ cells occupying either the entire or at least one-half of the gonads (Fig. 2a). Ten out of 20 females underwent complete sex reversal, and exuded sperm upon gentle pressure on the abdomen. In the sex-reversing fish, spermatogenic germ cells first appeared in the postero-ventral portion of the gonad, opposite to the main blood vessel. The ovarian cavity was situated in between the blood vessel and the newly-appeared spermatogenic cells. These fish had mature sperm and newly formed efferent ducts in the testicular region 908112-43-6 of their gonads; however, the 908112-43-6 ovarian cavity, an important characteristic feature of the female gonad, did not disintegrate upon sex reversal. Female tilapia receiving co-treatment of AI and E2 had ovaries with follicles at different stages of development.